A liquid crystal display device includes a liquid crystal display panel for displaying an image, and a driving unit for driving the liquid crystal display panel.
The liquid crystal display panel consists of a thin film transistor array (TFT) substrate and a color filter (CF) substrate soldered to face each other with a predetermined cell-gap, and a liquid crystal layer formed in the cell-gap between the TFT substrate and the CF substrate.
A plurality of gate lines are arranged to be separated at regular intervals in the horizontal direction and a plurality of data lines are arranged to be separated at regular intervals in the vertical direction such that they cross each other on the TFT substrate. The TFT substrate is divided into a plurality of rectangular regions by intersecting gate lines and the data lines. The rectangular regions are respectively defined as pixels. Each of the pixels includes a switching device such as a thin film transistor and a pixel electrode.
Red (R), green (G) and blue (B) CFs are formed on the CF substrate corresponding to the pixels. A black matrix for preventing color interference of light passing through the CFs is formed in a mesh shape to cover the outer sides of the CFs. And, a common electrode for supplying an electric field to the liquid crystal layer with the pixel electrodes of the TFT substrate is formed on the CF substrate.
The liquid crystal is driven by a vertical electric field applied between pixel electrodes and common electrodes. In the case of a twisted nematic (TN) liquid crystal display device, the light transmission is symmetrically distributed over a wide range in the right/left viewing angle, but asymmetrically distributed with respect to an up/down viewing angle, narrowing the viewing angle. Consequently, light transmission in a gray scale display is changed according to the viewing angle. As a result, the fabrication of a large area liquid crystal display panel is difficult.
In order to resolve the narrow viewing angle of the TN liquid crystal display device, an in-plane-switching (IPS) liquid-crystal display device has been suggested in which the pixel electrodes and the common electrodes are formed on the same surface, and which drives liquid crystals by a horizontal electric field between the pixel electrodes and the common electrodes.
As compared with the TN liquid crystal display device, the IPS liquid crystal display device improves contrast ratio (C/R), gray inversion and color shift, and thus obtains a wide viewing angle. In the liquid crystal display device, R, G and B pixels are sequentially and repeatedly arranged in the horizontal direction, and arranged in a stripe shape in the vertical direction, for displaying image information.
FIG. 1 is a plane view illustrating general pixel arrangement of a liquid crystal display device. A plurality of gate lines 11 arranged to be separated at regular intervals in the horizontal direction and a plurality of data lines 10 arranged to be separated at regular intervals in the vertical direction and cross each other on a substrate, thereby dividing the substrate into a plurality of rectangular regions defined as pixels. The pixels consist of red (R), green (G) and blue (B) color pixels. The R, G and B pixels P1 are sequentially and repeatedly arranged in the horizontal direction and arranged in a stripe shape in the vertical direction. In addition, switching devices T1 such as thin film transistors are individually disposed in the R, G and B pixels P1, and connected to the gate lines 11 and the data lines 10. The switching devices T1 are turned on by scan signals sequentially supplied to the gate lines 11. Image information supplied from the data lines 10 is transmitted to the R, G and B pixels P1 through the turned-on switching devices T1.
The liquid crystal display device represents one dot DOT of the image by combining light passing through the R, G and B pixels P1. One dot DOT consists of combinations of the R, G and B pixel P1.
As the liquid crystal display device having the aforementioned pixel arrangement displays the image through the rectangular DOT consisting of the R, G and B pixels P1, in the situation that a boundary of the image is formed in an oblique line or curved line, the oblique line or curved line is not smoothly displayed but displayed in a stair shape at the boundary of the image.
In order to resolve the above problems a triangular arrangement method for forming one DOT by R, G and B pixels P1 arranged in a triangular shape has been suggested.
FIG. 2A is a plane view illustrating triangular arrangement of the pixels of a liquid crystal display device. A plurality of gate lines 11 arranged parallel to each other in a zigzag shape in the horizontal direction and a plurality of data lines 10 arranged parallel to each other in a zigzag shape in the vertical direction cross each other, and R, G and B pixels P1 are arranged in a honeycomb shape in hexagonal regions formed by the gate lines 11 and the data lines 10. In addition, switching devices T1 are individually disposed in the R, G and B pixels P1. When scan signals are sequentially supplied to the gate lines 11, the switching devices transmit image information supplied through the data lines 10 to the R, G and B pixels P1.
The triangular arrangement of the pixels of liquid crystal display device for arranging the R, G and B pixels P1 in a honeycomb shape displays an image through a triangular dot DOT consisting of the R, G and B pixels P1. In the case that the boundary of the image is formed in an oblique line or curved line shape, the oblique line or curved line can be smoothly displayed in the boundary of the image. Such pixel arrangement is called a delta arrangement.
However, in the triangular arrangement liquid crystal display device for arranging the R, G and B pixels P1 in a honeycomb shape, the data lines 10 and the gate lines 11 are arranged in a zigzag shape, and thus have a larger line length than those in straight arrangement of the lines. Accordingly, image information or scan signals transmitted through the data lines 10 and the gate lines 11 may be distorted and delayed, which results in driving failure or a lower quality of image in the liquid crystal display device.
FIG. 2B is a circuit view illustrating an equivalent circuit of the triangularly-arranged pixels of FIG. 2a in the liquid crystal display device. A plurality of gate lines G1 to G4 are arranged in parallel in a zigzag shape in the horizontal direction, and a plurality of data lines D1 to D4 are arranged in parallel in a zigzag shape in the vertical direction. The gate lines G1 to G4 and the data lines D1 to D4 cross each other.
Hexagonal pixels P1 are arranged in a triangular shape to compose one DOT. Switching devices T1 for supplying image information to pixel electrodes 11 are disposed in the pixels P1.
Generally, thin film transistors are used as the switching devices T1. Gate electrodes of the thin film transistors are connected to the gate lines G1 to G4, source electrodes thereof are connected to the data lines D1 to D4, and drain electrodes thereof are connected to the pixel electrodes 11 of the pixels P1, respectively. Accordingly, when scan signals of the liquid crystal display device are sequentially supplied to the gate lines G1 to G4, the thin film transistors are turned on in a unit of gate line G1 to G4, and thus conductive channels are formed between the source electrodes and the drain electrodes. The image information supplied to the source electrodes of the thin film transistors through the data lines D1 to D4 is transmitted to the drain electrodes through the conductive channels. Here, the drain electrodes are connected to the pixel electrodes 11, and thus the image information is supplied to the pixel electrodes 11.
Common electrodes 13 are formed in the pixels P1 at regular intervals and disposed such that they are separated from the pixel electrodes. Common voltages are supplied to the common electrodes 13 of the pixels P1 through common voltage lines VL1. Because the common voltage lines VL1 are arranged in parallel to the gate lines G1 to G4 and electrically connected to each other, the same common voltages are supplied to all of the pixels P1. Therefore, a liquid crystal layer is driven by a horizontal electric field between the image information supplied to the pixel electrodes 11 and the common voltages supplied to the common electrodes 13.
Although not illustrated, the pixel electrodes 11 are electrically connected to storage capacitors disposed in each pixel. During the turn-on period of the thin film transistors in which the scan signals are supplied, the image information supplied to the pixel electrode 11 is charged in the storage capacitors. During the turn-off period of the thin film transistors in which the scan signals are not supplied, the charge representing image information is supplied to the pixel electrodes 11, to maintain the driving of the liquid crystal layer.
When a constant electric field is continuously supplied to the liquid crystal layer, liquid crystals deteriorate, and after images are formed when direct current voltage is used. In order to prevent deterioration of the liquid crystals, the voltages representing the image information are supplied to have alternating positive and negative polarities with respect to the common voltages. This driving method is called an inversion driving method.
Exemplary inversion driving methods include a frame inversion method for inverting polarity of image information on a frame-by-frame basis, a line inversion method for inverting polarity of image information in a line-by-line basis, and a dot inversion method for inverting polarity of image information both in each adjacent pixel and from frame-to-frame.
In the aforementioned inversion driving methods, the dot inversion method provides high image quality by restricting image distortion such as flicker or crosstalk in comparison with the other inversion methods. The dot inversion method will now be described in more detail with reference to the accompanying drawings.
FIG. 3 is an exemplary view illustrating voltage waveforms of pixels in the dot inversion driving method. Common voltages VCOM that are constant direct current voltages are supplied to common electrodes, and scan signals VG1 to VG3 are sequentially supplied to gate lines. Positive and negative polarities of image information VDATA are inverted in each adjacent pixel on the basis of the common voltages VCOM. In addition, the positive and negative polarities of the image information VDATA are inverted from frame-to-frame with respect to the common voltages VCOM.
During the turn-on period of thin film transistors in which the scan signals VG1 to VG3 are supplied with a high potential, the image information VDATA supplied to pixel electrodes is charged in storage capacitors with pixel voltage waveforms Vp. During the turn-off period of the thin film transistors in which the scan signals VG1 to VG3 are supplied with a low potential, the pixel voltages Vp which were charged in the storage capacitors are supplied to the pixel electrodes, to maintain the driving of the liquid crystals.
When the scan signals VG1 to VG3 transition to a low potential, the pixel voltages Vp are lowered due to parasitic capacitance coupling generated by overlapped gate electrodes and drain electrodes of the thin film transistors, which is represented as a fluctuation range ΔVp of the pixel voltages Vp.
Liquid crystal driving voltages Vcel for driving the liquid crystal layer are defined as voltages (VDATA-VCOM) obtained by subtracting the common voltages VCOM supplied to the common electrodes from the image information VDATA supplied to the pixel electrodes. Because the liquid crystals are driven by an electric field generated by the liquid crystal driving voltage Vcel, the conventional liquid crystal display device requires a high voltage level of the image information VDATA to display a target image, which results in high power consumption.
The common voltages are supplied to the common electrodes of the pixels and constantly maintained for one frame, and the image information is supplied to the adjacent data lines according to the dot inversion method for supplying different polarities of image information. The liquid crystals are driven by voltage differences between the image information and the common voltages.
FIG. 4 is an exemplary view illustrating polarity constitution of the pixels in the dot inversion driving method. Different polarities of image information are supplied to the adjacent pixels in accordance with to the dot inversion method, and different polarities of image information are supplied to the pixels in sequential frames.
In the conventional triangular arrangement liquid crystal display device, the data lines and the gate lines are arranged in a zigzag shape, and thus have an extended line length. Accordingly, the image information or scan signals transmitted through the data lines and the gate lines are distorted or delayed, which results in driving failure or a lower quality image of the liquid crystal display device. Furthermore, as the liquid crystal display device is driven by the inversion driving method, the liquid crystal driving voltages for driving the liquid crystals are defined as the voltages obtained by subtracting the common voltages from the image information. In order to display a target image, a high voltage level of the image information is required, and thus power consumption of the liquid crystal display device is increased.